To gain insight into the pathogenesis of oculomotor disease and strabismus, we are investigating the genetic basis of congenital eye movement disorders referred to as 'congenital cranial dysinnervation disorders' (CCDDs). We have proposed that the forms of CCDD with primary dysfunction of vertical eye movement, including CFEOM and ptosis, result from maldevelopment of oculomotor and trochlear nuclei and nerves, while the forms of CCDD with primary dysfunction of horizontal gaze, including Duane syndrome and horizontal gaze palsy, result from maldevelopment of the abducens nucleus and nerve. Thus far, we have defined six CCDD genetic loci (FEOM1-3, PTOS1, DRRS, DURS3) and identified all of the CCDD genes known to date (PHOX2A, SALL4, KIF21A, and ROBO3). Each of these genes appears to be essential to a specific step in the development of the ocular cranial nuclei, including axonal targeting of the motor neurons (ROBO3), motor neuron development (PHOX2A), and axonal targeting of the extraocular muscles (KIF21A). In this renewal application, we seek funding to continue our work to discover the genetic causes of vertical CCDDs beyond PHOX2A andKIF21A, including identification of the FEOM3 and PTOS1 genes. By identifying new genes mutated in complex vertical strabismus and ptosis we will define the genetic basis of these disorders, leading both to diagnostic testing for affected individuals and to new avenues of investigation into the pathogenesis of oculomotor disease and cranial nuclear, nerve, and muscle development. We will address the following aims: Aim 1. Identify the FEOM3 disease gene and analyze CFEOM pedigrees and sporadic individuals for disease-causing mutations. Aim 2. Identify the PTOS1 disease gene and analyze congenital ptosis pedigrees and sporadic individuals for disease-causing mutations. Aim 3. Identify new vertical CCDD loci by SNP-based genome screens of unmapped pedigrees. Aim 4. Initiate structural and functional characterization of the FEOM3 and PTOS1 genes and their protein products.